Support interpolating environment variables on /docker-entrypoint-initdb.d iql scripts

I would like to suggest supporting interpolating environment variables in initialization `*.iql` scripts found in `/docker-entrypoint-initdb.d`.

This can allow user creation queries while still interpolating the password from env vars

Start by examining how initialization *.iql scripts under /docker-entrypoint-initdb.d are discovered and executed in the Docker image. Determine the existing initialization path and how environment variables are handled; done means supported variables are interpolated for these scripts without breaking normal initialization.

Written by the indexing model from the issue text.